The present invention relates to improvements in worm centrifuges of the type having a rotatable outer drum and a rotatable inner conveying screw driven by independent drives with means for interconnecting the drives during start-up and one of the drives being a speed regulatable drive.
In centrifuge drives which have been used heretofore such as shown in German Laid Open Application 2,131,087 and German Allowed Application 1,178,791, the drive for the drum is not speed regulatable in contrast to the drive for the conveying screw. In the design and dimensioning of the drive for the drum, the high moment of inertia of the drum must be considered in the design of the asynchronous motors which are usually employed. The recognized heating caused by the respective current consumption and time have to be taken into consideration. In order to keep the start-up phase and the motor heating which occurs during the start-up phase within justifiable limits, asynchronous motors of correspondingly high power must be employed. However, after the start-up has been achieved, these are operated far below their nominal power in order to maintain a stationary operation of the centrifuge drum which results in poor efficiency. In contrast thereto, the use of a speed controlled motor for starting up the drum as is shown in Laid Open German Patent No. 2,849,547, makes possible a controlled slow start-up and a motor with lower power can be incorporated to satisfy requirments of energy of the operation after start-up has been accomplished. The slow start-up operation is without significance because of the lower start-up frequency of such centrifuges. Although a speed controllable drive is more expensive per se than an asynchronous motor, the centrifuge drive according to German Laid Open Patent No. 2,849,547 makes use of the fact that a speed controllable drive already exists for the worm drive. It is, therefore, proposed to also employ this drive for the conveying screw in starting up the centrifuge as well as operating the centrifuge after start-up has been accomplished. This will cover the further energy requirements by means of an asynchronous motor which can then be designed only in accord with the power required for the normal stationary operation and thus can be significantly smaller than known drives employed for this purpose.
An object of the invention is to further improve the centrifuge drive of German Laid Open Patent No. 2,849,547, particularly in providing better economics and better operation. With a centrifuge of the type referred to above, this objective is achieved by the present invention in that the output shafts of the separate drives used for the centrifuge drum and the conveying screw are directly connected to each other by a releasable coupling or clutch.
By this construction, structural changes which would otherwise be necessary at the centrifuge are eliminated. The arrangement of the present invention is also useful in the oonversion of older centrifuges since structural changes need only be undertaken in the area of the drive motors themselves. A start-up to the centrifuge by means of the speed controllable drive can be accomplished using the output shaft of the non-speed controllable drive for the drum which is on-line without being driven by the power drive for the drum during the start-up phase. The location or provision of a coupling between the shafts of the drive motors driving through the drive trains to the drum and screw permits at starting of the centrifuge a slip between the drum and screw corresponding to the gear ratio of the gearing in the drive to the drum or in the drive to the conveying screw if a ratio is used in the conveying screw drive. The advantages described above are important, particularly when solid components already exist in the drum before start-up. With this arrangement, a start-up with slip guarantees a conveying effect of the conveying screw in the direction toward the solids discharge of the drum directly at the beginning of the start-up operation so that plug-ups or material backups are prevented.
In one preferred form of the invention, the output shafts of both power means are connected to the drum and to the screw by means of belt drives with different drive ratios. By this arrangement, the belt drive connecting the output shaft of the drive means for the drum is a geared down or speed reduction drive. This geared down ratio results in increase of the effect of torque which is applied to the drum, and this is important at start-up due to the high moment of inertia of the drum. A further advantage, and in particular an economic advantage is present when a hydraulic system is employed as the speed controllable power means. For the existing geared down drive for the drum, this renders possible the employment of a high speed hydraulic engine or power means which requires only a small structural space and which can provide the same power output but is significantly more cost favorable than a low speed structure which generates a high torque. Thus, capital costs of the centrifuge drive can be appreciably reduced.
The objects and advantages of the invention will be more clearly understood in connection with the disclosure of the preferred embodiment in the single FIGURE of the drawing in which: